Electrical conductor coated with high temperature insulating varnishes



Aug 11 1970 ,H. E. 'HEFF 3,523,820

ELECTRICAL C UCTOR TED WI HIGH TEMPERATURE NSULATING vmmsnms Filed April18, 1966 BY %%%%M ATTORNEYS United States Patent U.S. Cl. 117-218 6Claims ABSTRACT OF THE DISCLOSURE Electrical conductors having improvedproperties at high temperature are produced by providing such conductorswith three resinous coatings, the second coating being polyethyleneterephthalate or linear polyimidepolyamides.

This invention relates to oil-modified alkyd resins and insulatingvarnishes containing such resins as Well as to electrical conductorscoated with such varnishes.

It has previously been proposed to prepare insulating varnishes fromshort oil-modified glyceryl isophthalate and an oil-solublephenol-formaldehyde resin, Thielking Pat. No. 3,080,331. Such a varnishis quite valuable but, unfortunately, cannot be employed where the finalproduct must be classified as 180 C. (Class H) in the AIEE No. 57 heatlife test.

It is an object of the present invention to prepare a novel oil-modifiedalkyd resin.

Another object is to prepare an insulating varnish suitable forcontinuous use at 180 C.

An additional object is to develop an improved wire having an polyesteror polyimide under coat and a Dacron top coat and a protective coat ofinsulating varnish over the top coat.

A further object is to prepare an enameled wire having improvedproperties in the burnout test.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by Way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

It has now been found that these objects can be at tained by preparinginsulating varnishes containing alkyd resin from isophthalic acid, tris(Z-hydroxyethyl) isocyanurate and drying oil acids. Preferably thedrying oil acids do not have substantially more unsaturation thansoybean oil acids. In addition to the oil-modified alkyd resin thereshould be present an oil-soluble phenol-formaldehyde resin in an amountof 10' to 80% of the total of the alkyd resin and phenolic resin. Inplace of isophthalic acid less preferably there can be used terephthalicacid in the higher oil length ranges, e.g. a 55% oil length.

A portion of the tris (Z-hydroxyethyl) isocyanurate (THEI) can bereplaced by another polyol, e.g. glycerine or pentaerythritol. Thus, theTHEI can be 50 to 100% of the total polyol. However, it should berealized that replacing part of the THEI by another polyol will impairto some extent the improved thermal properties of the varnishes of thepresent invention.

As the drying oil acids there can be used soybean oil acids, cottonseedoil acids, corn oil acids, whale oil acids, safllower oil acids orsunflower oil acids, or less preferably, linseed oil acids, tung oilacids, oiticica oil acids, perilla oil acids.

A portion of the drying or semi-drying oil acids can 3523,82 PatentedAug. 11, 1970 "ice be replaced by non-drying oil acids such as coconutoil fatty acids, oilve oil acids, castor oil acids, peanut oil acids andrapeseed oil acids.

When a portion of the THEI is replaced by glycerine the latter need notbe added as such but can be added in the form of an oil, e.g. soybeanoil, corn oil, linseed oil, or the like. In such case, of course, theoil supplies part or all of the oil fatty acid component.

The oil-modified alkyd resin can include 20 to 65% of the fatty acidsbut preferably contains 30 to 55% of the fatty acids, e.g. soybean fattyacids.

Unless otherwise indicated, all parts and percentages are by weight.

The invention will be understood best in connection with the drawingswherein the single figure is a crosssectional view of an electricalconductor having an insulating coating according to the invention.

Referring more specifically to the drawings, there is provided anelectrical conductor, e.g. a wire 2 having a first (or under coat)continuous coating 4 of a polymeric ester of terephthalic acid and tris(Z-hydroxyethyl) isocyanurate, a second (or top coat) continuous coating6 of polyethylene terephthalate and a protective coat 8 of soybean oilfatty acid modified polymeric ester of isophthalic acid and tris(Z-hydroxyethyl) isocyanurate admixed With p-t-butylphenol formaldehyderesin.

As the under coat there is employed a polyester or polyimide suitablefor continuous use at C. or above.

The polyester employed in forming the under coat is the reaction productof a polymeric ester of terephthalic acid or isophthalic acid with THEI.A portion of the THEI, up to 50% of the total polyhydric alcohol on aweight basis can be replaced by a modifying polyhydric alcohol such asethylene glycol, butanediol-l,4, pentanediol 1,5, butene-2-diol-1,4,butyne-2-diol-l,4; 2,2,4,4- tetramethyl-1,3-cyclobutanediol,1,4-cyclohexanedimethanol, hydroquinone di-B-hydroxyethyl ether,glycerine, trimethylolethane, 1,1,1-trimethylolpropane, pentaerythritol,dipentaerythritol, sorbitol or mannitol.

A portion of the terephthalic acid or isophthalic acid up to 50equivalent percent of the acid component can be replaced by a modifyingpolycarboxylic acid such as o-phthalic anhydride, adipic acid, sebacicacid, hemimellitic acid, trimellitic acid, trimesic acid, succinic acid,tetrachlorophthalic anhydride or hexachloroendomethylenetetrahydrophthalic acid.

The total number of hydroxyl groups on the alcohols normally is 1 to 1.6times the total number of carboxyl groups on the acids in the undercoat.

The polyester can also be modified by adding an organo titanate and/or apolyisocyanate.

As the titanate there can be used tetraalkyl titanates such astetraisopropyl titanate, tetrabutyl titanate, tetramethyl titanate,tetrahexyl titanate and tetrapropyl titanate. The titanate is used in anamount of 0.001 to 4.0% titanium metal on the total solids of the undercoat.

As the polyisocyanate there can be used 2,4-tolylene diisocyanate,2,6-tolylene diisocyanate, hexamethylene diisocyanate, blockedisocyanates such as the reaction product of three mols of mixed 2,4- and2,6-tolylene diisocyanates with trimethylol propane and blocked byesterification with phenol (Mondur S), and the cyclic trimers of 2,4-and 2,6-tolylene diisocyanates having the three free isocyanate groupsblocked by esterification with m-cresol (Mondur SH). There can be usedany of the polyisocyanates, including the blocked isocyanates, set forthin Sheffer et al. Pat. No. 2,982,754, or in Meyer et al. Pat. No.3,211,585. Usually I to 40% of the total solids are polyisocyanates.

The polyester under coat can be applied to the electrical conductor inthe manner disclosed in Meyer et al. Pat. No. 3,211,585, and Meyer etal. Pat. No. 3,201,276. As

the polyester under coat there can be used any of the THEI containingterephthalates of the two Meyer et al. patents as well as thecorresponding isophthalates.

In place of using a polyester as an under coat, there can be used apolyester-polyimide in which at least 20%, and preferably at least 50%,of the alcohol component of the polyester is THEI and the polybasic acidcomponent comprises terephthalic acid, isophthalic acid or benzo phenonedicarboxylic acid. The polyimide component of the molecule normally hasa member of the group consisting of benzene and naphthalene rings joinedto two carbon atoms of a heterocyclic imide ring having to 6 members inthe ring, one of the atoms in the heterocyclic ring being nitrogen andthe balance carbon.

The usual components of the polyester-polyimide are (1) an aromatic oraliphatic diamine, e.g. methylene dianiline, oxydianiline, benzidine,3,3-diamin0-diphenyl, pphenylene diamine, 1,4diamino-naphthalene, a,W-nonamethylene diamine, 4,4-diaminodiphenyl ether, heptamethylenediamine, diamino-diphenyl ketone, hexamethylenc diamine, ethylenediamine, diamino-diphenyl sulfone, 4,4'-dicyclohexylmcthane diamine, (2)an anhydride having 3 to 4 carboxyl groups such as trimelliticanhydride, pyromellitic dianhydride, benzophenone 2,3-,2',3'-tetracarboxylic dianhydride, 2,3,6,7-naphthalene dianhydride and3,3',4,4-diphenyl tetracarboxylic dianhydride, (3) a dibasic acid suchas terephthalic acid, isophthalic acid or benzophenone dicarboxylicacid, and (4) a polyhydric alcohol containing at least THEI. Thepolyesterpolyimide preferably contains 5 to 50% polyimide groups basedon the total of the polyester and polyimide groups.

There can be employed any of the polyester-polyimides disclosed in Meyeret al. application Ser. No. 457,474, filed May 20, 1965, now Pat.3,426,098, and the under coat can be applied to the electrical conductoras set forth in that application. As disclosed in that Meyer et al.application, there can be employed as modifiers the same polyisocyanatesin an amount of 1 to and alkyl titanates in an amount of l to 10% asmentioned in the Meyer et a1. Pat. No. 3,211,585 and Sheffer et al. Pat.No. 2,982,754.

The under coat, whether it is a polyester of polyesterpolyimide, alsousually contains 1 to 5% based on the total solids of amelamine-formaldehyde resin or a phenolic resin such asphenol-formaldehyde, cresol-formaldehyde or xylenol-formaldehyde resin.

As the top coat there is preferably employed polyethylene tercphthalate.It is applied from a solvent solution, as set forth in Meyer et a1. Pat.No. 3,201,276. The preferred solvent contains to of monochlorophenol andthe balance a cresol or mixture of cresol with phenol.

In place of polyethylene terephthalate there can be employed as the topcoat polyimide-polyamides, polyesterpolyimidamicies, straight polyimidesand other linear polymers. Thus, there can be used the pyromellitimideavailable commercially as Pyre-ML as well as other polyimides such asthe reaction product of 3,3'-diaminodiphenyl and pyromellitic anhydride,the reaction product of oxydianiline with pyromellitic anhydride, thereaction product of methylene dianiline with pyromellitic anhydride orthe polyimides disclosed in Edwards Pat. No. 3,179,634, thepolyester-polyimide-polyamide from ethylene glycol, terephthalic acid,methylene dianiline and pyromellitic anhydride, etc. There can also beused polyesters such as polyhexamethylene glycol terephthalate and otherlinear polyesters.

The insulating varnishes of the present invention can be applieddirectly to electrical conductors but are preferably employed as aprotective coat over the under coat and top coat formulations justdescribed. The insulating varnishes can be used to coat copper, aluminumand silver wires and to impregnate armature and field coils of motorsand for both power and distribution transformers of either the oil ordry type where long life at high operating temperatures is required.While the insulating varnishes of Thielking Pat. No. 3,080,331 areindicated as being suitable only at temperatures of up to C. theinsulating varnishes of the present invention are suitable forcontinuous use at temperatures of C. and higher.

In addition to the higher fatty acid modified THEI polyester asindicated the varnish also includes an oilsoluble phenol-formaldehyderesin. The preferred phenols for forming these phenol-formaldehyderesins are ortho and para alkyl substituted phenols, 2,2-bis(phydroxyphenyl) propane and 4,4-bis (p-hydroxyphenyl) propane.

As examples of suitable phenols for making the resin, mention can bemade of p-t-hutylphenol, p-tamylphenol, p-t-octylphenol, p-phenylphenol,o-t-butylphenol, and the phenols of Honel Pat. No. 1,800,296. Any of theoilsoluble phenol aldehyde resins set forth in the Thielking patent canbe employed.

The insulating varnish contains conventional varnish solvents inaddition to the resin components. Such solvents include one or more ofxylene, mineral spirits, isophorone, naphtha, toluene and benzene.

EXAMPLE 1 762 grams of soybean oil fatty acids (Emery 610 soy oil fattyacids), 945 grams of tris(2-hydroxyethyl) isocyanurate and 597 grams ofisophthalic acid were loaded in a flask, the temperature raised in onehour to 440 F. and held in the 440-470 F. range for 3.5 hours until theacid number was 25. The batch was thinned with 2000 grams of xylene toZ7 viscosity at 50% solids to give a 41% oil length alkyd resin.

To 575 grams of the alkyd resin was added 145 grams ofp-t-butylphenol-formaldehyde resin (46B phenolic resin) at 50% solids inxylene and 80 grams of additional xylene. The final viscosity of theinsulating varnish thus obtained was T (550 cps.) at 45% solids.

EXAMPLE 2 1344 grams of soybean oil fatty acids (Emery 610 soy oil fattyacids), 885 grams of THEI and 348 grams of isophthalic acid were loadedin a flask and the temperature raised to 480 F. in 3.5 hours. The batchwas then heated in the 480520 F. for 4.5 hours until the acid number was6. The batch was thinned with 1350 grams of aromatic naphtha to Zviscosity at 65% solids.

To 1158 grams of this alkyd resin were added 1500 grams ofp-t-butylphenol-formaldehyde resin and 342 grams of aromatic naphtha.The final viscosity of the insulating varnish thus produced was G at 50%solids.

EXAMPLE 3 An insulating varnish was prepared similar to that of Example1 but using an alkyd resin made from 387 grams of soybean oil fattyacids, 243 grams of coconut oil fatty acids, 597 grams of isophthalicacid and 945 grams of THEI.

EXAMPLE 4 A motor stator was impregnated with the insulating varnish ofExample 1 in a dip tank operation. The varnish was cured by baking in anoven at 395 F. for 1 hour.

EXAMPLE 5 No. 18 copper wire was coated with Isonel 200E and then givena top coat of polyethylene terephthalate (Isonel 17) in conventionalfashion. Isonel 200E is the mixture of (a) 86 parts of the polyesterfrom 4400 parts of THEI, 481 parts of ethylene glycol and 5019 parts ofdimcthyl terephthalate, (b) 5 parts of Mondur SH, (e) 5 parts oftetraisopropyl titanate and (d) 5 parts of m-p-cresolformaldehyde resin(made from 3440 parts of m-p-cresol and 1962 parts of 37% aqueousformaldehyde).

The thus coated wire was dipped twice through the in sulating varnishprepared in Example 1 with curing at 395 F. for 1 hour after each dip.The wire having the three coatings was tested by AIEE No. 57 twistedpairs with the following results:

Temp. C.: Hours to failure at 1000 volts 280 268 This data extrapolatesto 180 C. for 20,000 hours which shows that the system of the fatty acidalkyd insulating varnish, polyethylene terephthalate top coat and Isonel200 under coat had a Class H rating. The product had improved bondingstrength and less weight loss than a conventional top coated Isonel 200wire enamel which was not further coated with the fatty acid modifiedalkyd resin varnish.

EXAMPLE 6 The same procedure as that of Example 5 was repeated but usingthe insulating varnish of Example 2 to obtain a coated wire which had aClass H rating.

EXAMPLE 7 It was also found that the insulating varnish of Example 2applied to wire coated with Isonel 200E and topcoated with polyethyleneterephthalate (Isonel 17) gave improved results in the burnout test. Theburnout test is run by twisting pairs of the enameled wire, dipping inthe varnish and curing for 1 hour at 400 P. Then 33 amperes is appliedfor four minutes and the breakdown voltage of the system tested. Theresults obtained in the burnout tests were as follows, final voltageswere expressed in kilovolts.

Without With varnish varnish Isonel 17 over Isonel 200 E 4. 98 8. 6Isonel 17 over Isomid 0.77 2. 38 Isomid 0.75 1.16

ester of tris (2-hydroxyethyl) isocyanurate and an aromatic dicarboxylicacid and (2) a polyester polymide wherein at least 20% of the alcoholcomponent of the polyester is tris (Z-hydroxyethyl) isocyanurate, asecond coating selected from the group consisting of (1) linearpolyethylene terephthalate, (2) and linear polyimide-polyamides, and athird coating of an insulating varnish including (a) an alkyd resinselected from the group consisting of unsaturated higher fatty acidmodified tris (2-hydroxyethyl) isocyanurate isophthalate and unsaturatedhigher fatty acid modified tris (Z-hydroxyethyl) isocyanurateterephthalate, said resin having 20 to of higher fatty acids, and (b) anoil soluble phenol-formaldehyde resin, the phenol-formaldehyde resinbeing present in an amount of to 15% of the total of the alkyd resin andphenolformaldehyde resin over said coating.

2. An electrical conductor according to claim 1, wherein the secondcoating is polyethylene terephthalate, said conductor having said threecoatings, having a heat life at C. of at least 20,000 hours.

3. An electrical conductor according to claim 2, wherein the alkyd resinis an isophthalate.

4. An electrical conductor according to claim 2, wherein the firstcoating is a continuous coating of a polyesterpolyimide.

5. An electrical conductor according to claim 2, wherein the firstcoating is a continuous coating of a polyester of an aromatic acidselected from the group consisting of terephthalic acid, isophthalicacid and benzophenone dicarboxylic acid.

6. An electrical conductor according to claim 1, Wherein the secondcoating is a linear polyimide-polyamide.

References Cited UNITED STATES PATENTS 3,201,276 8/1965 Meyer et al117218 3,297,785 l/19 67 George et al 260-22 3,312,573 4/1967 Sheifer117218 3,312,645 4/ 1967 George et a1. 260 22 3,428,486 2/1969 George 117-218 FOREIGN PATENTS 1,046,910 10/ 1966 Great Britain. 1,322,055 2/1963 France.

DONALD E. CZAJ A, Primary Examiner R. W. GRIFFIN, Assistant Examiner US.Cl. X.R.

ll7-l28.4, 161, 232; 260 -20, 22, 33.6

